Do Not Treat SMTPUTF8-Related Delivery Failures as Hard Bounces by Default

Hi Listmonk team, I'd like to suggest improving how Listmonk classifies SMTP delivery failures, particularly SMTPUTF8-related errors. I encountered the following bounce report when sending a campaign: Reporting-MTA: dns;server.reidcompound.net X-MTA-ID: ftk2ln7e9nbv dedi-mta-uid-17-m6tgq Received-From-MTA: dns;localhost (152.53.240.200) Arrival-Date: Tue, 27 Oct 2026 15:42:40 +0000 Final-Recipient: rfc822;[email protected] Action: failed Status: 5.6.7 (destination does not support SMTPUTF8 required for message delivery) Remote-MTA: dns;mailsec.protonmail.ch (185.70.42.129) X-MTA-BounceCategory-Name: content-related bounce mail content: Hello, this is the mail server on server.reidcompound.net. I am sending you this message to inform you on the delivery status of a message you previously sent. Immediately below you will find a list of the affected recipients; also attached is a Delivery Status Notification (DSN) report in standard format, as well as the headers of the origin…